As disclosed for example by Palmaz U.S. Pat. No. 4,733,665 expandable grafts or stents may be implanted into the vascular system of a patient to prevent collapse of the lumen of a segment of a vein or particularly an artery. Such grafts or stents are typically made of tubular wire mesh which initially begin at a reduced outer diameter and are carried about an expansion balloon of an angioplasty catheter. Then, when the stent is properly positioned, the balloon is expanded to enlarge the diameter of the wire mesh stent. Once the diameter of the wire mesh stent is so enlarged, the stent is basically locked by one of a variety of known prior art techniques so that it does not collapse again after the balloon is deflated and the catheter withdrawn.
While a large variety of such stents and stent emplacement systems are known as prior art, the respective prior art systems exhibit the disadvantage that, naturally, a catheter balloon which carries a stent has a larger outer diameter than the smallest deflated angioplasty catheter balloons. Thus, particularly in the case of a very tight stenosis in an artery, it may not be possible to emplace the deflated angioplasty balloon and its carried stent into the stenosis, as would be desirable so that the stenosis may be expanded, and then the stent may be emplaced to prevent recollapse of the stenosis, for example as part of a PTCA procedure.
In such a circumstance, in the prior art it may be necessary for the surgeon to pass through the stenosis with a catheter having a relatively small dilatation balloon on a guidewire. Then, after expanding the stenosis with a small dilatation balloon, that catheter has to be withdrawn, and another catheter, having a larger dilatation balloon and carrying the stent, must be advanced to pass into the stenosis which has been partially expanded.
Such a procedure is of course inconvenient and difficult, requiring two catheters. Also, sometimes during the period between the withdrawal of the first catheter and the advancement of the second catheter the stenosis can recollapse, so that it remains impossible to get the stent and its typically larger balloon through the stenosis despite the initial expansion action of the smaller balloon of the first catheter.
The catheter of this invention addresses the disadvantages found in the prior art, providing a single catheter which is capable of penetrating very narrow, tight stenoses where only a very small lumen remains, yet which is also capable of expanding a stent to a diameter larger than the inflated diameter of the initial, small balloon which penetrates the stenosis. Thus, a double advantage is provided by the catheter of this invention, in that it is capable of penetrating very tight stenoses, but also it is capable of expanding and emplacing a stent of large enough diameter that the small balloon that initially penetrates the stenosis could not be used to expand the stent to the desired diameter.